The typical internal combustion engine is cooled by providing a coolant (oftentimes called anti-freeze) in cavities that surround the engine. A typical coolant is an aqueous glycol composition such as aqueous ethylene glycol or propylene glycol. These glycols function to reduce the freezing point of coolant and raise the coolant's boiling point, thus assuring that the vehicle's coolant will not freeze or boil over. During operation of the engine, air is constantly drawn into and expelled from the coolant composition. When the coolant is heated during engine operation, air is expelled from the coolant. When the engine is at rest and the temperature of the coolant drops, air is absorbed by the coolant up to the saturation point. This repeated cycle in the life of a coolant provides an oxidation mechanism by which metal ions that are generated by corrosive attack of engine surfaces are subjected to instantaneous oxidation and glycol is thermally oxidized.
Essentially all metal ions when converted to their highest oxidation state form insoluble hydroxides and oxides in the coolant composition, thus forming a precipitate that collects within the engine's coolant chamber. Some of the metals are oxidized to form precipitated hydroxides that deposit on the wall of the coolant chamber and interreact by condensation reactions to form a beneficial oxide layer. This layer protects the engine block from serious corrosion. It would be undesirable to have present in the coolant a component that attacks that beneficial oxide layer and causes its removal. Such action eventually leads to serious corrosion of the engine block. One such component that would attack the beneficial coating if present in the coolant in deleterious amounts, is the chloride ion. It will convert the oxides into soluble chlorides, thus wiping away the beneficial oxide layer. For example, it will convert iron oxides through thermally induced chlorination, to ferric and ferrous chlorides, and aluminum oxides through thermally induced chlorination, to aluminum chloride. These chlorides are very acidic and notorious Friedel-Craft catalysts. They can accelerate the decomposition of the coolant and cause corrosion of metal surfaces.
Other of the precipitates form within the coolant and serve no useful function. Most of these precipitates are of sufficient size so as to deposit from the coolant to the bottom of the coolant chamber. A minor portion, more like a trace amount, of the precipitates have such a small size (more like microscopic in size) that they remain dispersed in the coolant. Eventually these precipitates have to be removed and thus flushing of the coolant system is an appropriate procedure.
The trace amounts of these metal hydroxides that remain suspended particulates within the coolant will, with time, chemically interreact to form dimeric and oligomeric condensates. Such condensates remain suspended (dispersed) in the coolant. These condensates are difficult to remove by filtration because they have an extremely small particle size. Because the metal atoms in these condensates are at their maximum state of oxidation, further oxidation of the coolant will not cause these condensates to be further oxidized. Nor will further oxidation cause these condensates to drop out of dispersion in the coolant.
There are described in the literature a variety of systems directed to the treatment of spent engine coolant that allows for the recovery and refurbishing of such coolant. Illustrative of such technology are a series of patents to the Wynn Oil Company, such as U.S. Pat. Nos. 4,083,393, 4,091,865, 4,109,703, 4,178,134, 4,209,063, 4,293,031, 4,791,890, 4,793,403, 4,809,769, 4,899,807, 4,901,786, 5,021,152, 5,078,866, 5,306,430, 5,318,700 and Re. 31,274.
PCT/US92/00555 and U.S. Pat. No. 4,946,593, to Miller, describe a process for the treatment of a spent coolant outside of the engine.
A system that was commercialized in the past was sold by ECP, Inc., Westchester, Ill. It involved the vacuum removal of spent coolant from an engine, subjecting the coolant to filtration, and the addition of a "Coolant System Protector" to the filtered spent coolant.
Woyciesjes, et al., U.S. Pat. No. 5,223,144, describe a process for treating an aqueous spent coolant composition by adjusting its pH to the acid range, e.g., 4.0-7.5, by adding an acid, and then adding acid salts to effect precipitation of heavy metal impurities in salt or complex form from the spent coolant. Also included in the process description is the treatment of the acidic coolant composition with coagulating and flocculating agents, filtration of the acidic coolant, passing the acidic coolant through an activated carbon bed, through a distillation step, and a skimming step to remove precipitates.
A vehicle coolant recycling device is described by U.S. Pat. No. 5,549,832 to Ische, et al. The assignee of this patent is Century Manufacturing Company of Minneapolis, Minn.